Technical Field
The present application is based on Japanese Application No. 2013-005769 filed on Jan. 16, 2013, the entire contents of which are hereby incorporated by reference.
The present invention relates to a method for manufacturing an insulated wire and a manufacturing apparatus of the same.
Description of Related Art
An insulated wire is used for a coil of electric equipment such as a motor and a transformer. The insulated wire includes a conductor and an insulated coating film (insulated layer) formed on an outer periphery of the conductor. As the insulated wire, a round type electric wire using approximately circular conductor in cross-section, and a square electric wire (called a square conductor hereafter) using approximately a rectangular conductor in cross-section, can be given, which can be selected according to a purpose of use and a shape of the coil.
The insulated wire is manufactured while running the conductor as shown below at a specific speed. First, the conductor is run by a running machine to obtain a running wire. The running wire thus obtained is introduced to a coating material discharging tank, to thereby coat an outer periphery of the running wire with an insulation coating material. Next, the running wire coated with the insulation coating material is introduced to an incinerator, and the insulation coating material is baked and cured, to thereby obtain an insulated layer. Then, these steps are repeated multiple numbers of times until the insulated layer has a specific thickness, to thereby obtain an insulated wire (for example, see patent reference 1).
In recent years, miniaturization of the electric equipment such as a motor and a transformer is requested, and miniaturization is also required for the coil used for them. Owing to such a miniaturization of the coil, a space factor of the insulated wire can be improved. In order to improve the space factor, the square electric wire is more frequently used than the round type electric wire as the insulated wire, and the insulated layer is requested to be thin and uniform.
However, when the insulated wire is manufactured, and particularly when the square electric wire is manufactured, there is a problem that a coating of the formed insulated layer is easily ununiform, even in a case of a uniform coating of the insulation coating material. Namely, a thickness of the insulated layer in a peripheral direction of the insulated wire is easily ununiform. Such a phenomenon is generated, because the insulation coating material used for coating flows by surface tension before being cured, which is then cured in this state. For example, when the square conductor are uniformly coated with the insulation coating material, the thickness becomes small because the insulation coating material flows by the surface tension at a corner section of the square conductor, and meanwhile, at a planar section interposing the corner section, the thickness is large by swelling caused by the insulation coating material flowed from the corner section. Thus, by curing of the insulation coating material in a flowing state, the thickness of the formed insulated layer becomes ununiform.
As a method of improving the coating of the insulated layer, there is a method of increasing a viscosity of the insulation coating material and suppressing the flow of the insulation coating material by surface tension.
Patent reference 1: Japanese Patent Laid Open Publication No. 2002-109974